In a wireless communication system, such as universal mobile telecommunication services (UMTS) terrestrial radio access (UTRA), a wireless transmit/receive unit (WTRU) sends a channel quality indicator (CQI), (or channel quality estimates), to a base station. The CQI is used for adaptive modulation and coding (AMC), channel sensitive scheduling, or the like. The base station determines an optimal modulation scheme and coding rate for the WTRUs based on the reported CQIs. The base station also uses the reported CQIs when determining which WTRUs should be allowed for transmission.
The frequency of generation and transmission of the CQIs is controlled by parameters specified by a radio network controller (RNC). The parameters are given to the WTRU through radio resource control (RRC) signaling at call setup or upon reconfiguration.
The transmission of CQIs by the WTRUs, although beneficial for optimizing the capacity on the downlink, generates interference on the uplink. This interference may decrease the uplink capacity of the wireless communication system when the number of WTRUs that are required to transmit a CQI is large. Furthermore, it is often the case that the transmission of CQIs by certain WTRUs is superfluous. Such a situation arises when a WTRU has no pending transmission on the downlink due to a period of inactivity at the application level.
The interference caused by the transmission of CQIs from non-active WTRUs may be reduced by updating the CQI parameters so that the CQIs are generated by those WTRUs less frequently. However, this approach does not work well in practice because the CQI parameter update is performed through the RRC signaling, which is slow. By the time the CQI parameter update is communicated to the WTRU, the user of the WTRU may have resumed activity, and performance would suffer until a new update is sent to restore the original frequency of CQI generation.
In addition, in some circumstances it is desirable to reduce the interference from CQI transmissions during a limited period of time in order to increase the capacity available on the uplink when there is a temporary need for more capacity, (e.g., when one user has a large amount of data to upload, such as a picture).
Therefore, it is desirable to provide a method to adjust the CQI feedback period more quickly and efficiently to increase uplink capacity.